This invention relates generally to the field of digitally controlled printing devices, and in particular to continuous ink jet printers in which a liquid ink stream breaks into drops, some of which are selectively deflected.
Ink jet printing has become recognized as a prominent contender in the digitally controlled, electronic printing arena because, e.g., of its non-impact, low-noise characteristics, its use of plain paper and its avoidance of toner transfers and fixing. Ink jet printing mechanisms can be categorized as either continuous ink jet or drop on demand ink jet.
Conventional continuous ink jet printheads utilize electrostatic charging tunnels that are placed close to the point where the drops are formed in a stream. In this manner individual drops may be charged. The charged drops may be deflected downstream by the presence of deflector plates that have a large potential difference between them. A catcher (sometimes referred to as a xe2x80x9cgutterxe2x80x9d, an xe2x80x9cinterceptorxe2x80x9d, or a xe2x80x9ccollectorxe2x80x9d) may be used to intercept either the charged or the uncharged drops, while the non-intercepted drops are free to strike a receiver or recording medium. U.S. Pat. No. 3,878,519, issued to Eaton on Apr. 15, 1975, and U.S. Pat. No. 4,050,077, issued to Yamada et al. on Sep. 20, 1977, disclose devices for synchronizing drop formation in a liquid stream using electrostatic deflection by a charging tunnel and deflection plates. These devices require large spatial distances (sometimes referred to as xe2x80x9cink drop trajectory distancexe2x80x9d) between the printhead and the recording medium because the charging tunnel and deflection plates must be accommodated for within the device. As the amount of ink drop deflection is small, the ink drops need to travel over these large spatial distances in order to deflect enough to strike the recording medium (or the catcher). Ink drop placement accuracy is adversely affected when ink drops travel over large spatial distances because there is a greater risk of the drops being interfered within a manner that alters the drops"" path.
Alternatively, continuous ink jet printers may incorporate the charging tunnel and deflection plates in other printer components. U.S. Pat. No. 5,105,205, issued to Fagerquist on Apr. 14, 1992, and U.S. Pat. No. 5,469,202, issued to Stephens on Nov. 21, 1995, disclose devices of this type. Individual ink drops receive an electrical charge. An opposite electrical charge is applied to the surface of a catcher parallel to the normal trajectory of the ink stream. The opposite polarities create an attraction force that deflects the drops toward and onto the surface of the catcher. However, the amount of deflection is small. This configuration also requires large spatial distances between the printhead and the recording medium. This adversely affects ink drop trajectory distance as discussed above. As such, there is a need to minimize the distance an ink drop must travel before striking the print media in order to insure high quality images.
Referring to FIG. 2A, a printhead 200 includes a pressurized ink source 202 and a selection device 204. Printhead 200 is operable to form selected ink drops 206 and non-selected ink drops 208. Selected ink drops 206 flow along a selected ink path 210 ultimately striking recording medium 212, while nonselected ink drops 208 flow along a non-selected ink path 214 ultimately striking a catcher 216. Non-selected ink drops 208 are recycled or disposed of through an ink removal channel 218 formed in catcher 216. U.S. Pat. No. 6,079,821, issued to Chwalek et al. on Jun. 27, 2000 discloses an ink jet printer of this type.
While the ink jet printer disclosed in Chwalek et al. works extremely well for its intended purpose, ink drop path divergence (shown generally at 220), also commonly referred to as ink drop divergence angle (shown generally at angle A) or ink drop discrimination, between selected ink drops 206 and non-selected ink drops 208 is small. This, combined with other printhead environmental operating factors (inconsistent ink drop deflection 221 due to ink build up around heater 204, etc.), increases the potential for ink 222 to build up on catcher 216. As ink 222 builds up on catcher 216, selected ink drops 206 flowing along selected ink path 210 may be interfered with resulting in reduced image quality. As such, there is a need to increase ink drop path divergence in order to insure high quality images.
Continuous ink jet printers (page width, scanning, etc.) using electrostatic means to affect ink drop trajectory also experience ink build up on catcher surfaces. Ink that has built up on the catcher can become contaminated with paper dust, dirt, debris, etc., due to the operating environment of the printer. This causes clogging of the catcher. When this happens, the catcher must be thoroughly cleaned prior to operating the ink jet system. Additionally, contaminated ink must be cleaned before the ink can be reused, adding to the overall cost and expense of an ink jet system. As such, there is a need to increase ink drop path divergence in order to reduce printhead maintenance and ink cleaning.
U.S. Pat. No. 3,709,432, which issued to Robertson, discloses a method and apparatus for stimulating a filament of working fluid causing the working fluid to break up into uniformly spaced drops through the use of transducers. The lengths of the filaments before they break up into drops are regulated by controlling the stimulation energy supplied to the transducers, with high amplitude stimulation resulting in short filaments and low amplitudes resulting in long filaments. A flow of air is generated across the paths of the fluid at a point intermediate to the ends of the long and short filaments. The air flow affects the trajectories of the filaments before they break up into drops more than it affects the trajectories of the drops themselves. By controlling the lengths of the filaments, the trajectories of the drops can be controlled, or switched from one path to another. As such, some drops may be directed into a catcher while allowing other drops to be applied to a receiving member.
While this method does not rely on electrostatic means to affect the trajectory of drops it does rely on the precise control of the break off points of the filaments and the placement of the air flow intermediate to these break off points. Such a system is difficult to manufacture. Furthermore, the physical separation or amount of discrimination between the two drop paths is small increasing the difficulty of controlling printed and non-printed ink drops resulting in at least the ink drop build up problem discussed above.
U.S. Pat. No. 4,190,844, issued to Taylor on Feb. 26, 1980, discloses a continuous ink jet printer having a first pneumatic deflector for deflecting non-printed ink drops to a catcher and a second pneumatic deflector for oscillating printed ink drops. The first pneumatic deflector is an xe2x80x9con/offxe2x80x9d or an xe2x80x9copen/closedxe2x80x9d type having a diaphram that either opens or closes a nozzle depending on one of two distinct electrical signals received from a central control unit. This determines whether the ink drop is to be printed or non-printed. The second pneumatic deflector is a continuous type having a diaphram that varies the amount a nozzle is open depending on a varying electrical signal received the central control unit. This oscillates printed ink drops so that characters may be printed one character at a time. If only the first pneumatic deflector is used, characters are created one line at a time, being built up by repeated traverses of the printhead.
While this method does not rely on electrostatic means to affect the trajectory of drops it does rely on the precise control and timing of the first (xe2x80x9copen/closedxe2x80x9d) pneumatic deflector to create printed and non-printed ink drops. Such a system is difficult to manufacture and accurately control resulting in at least the ink drop build up discussed above. Furthermore, the physical separation or amount of discrimination between the two drop paths is erratic due to the precise timing requirements increasing the difficulty of controlling printed and non-printed ink drops resulting in poor ink drop trajectory control and at least the ink drop build up discussed above.
Additionally, using two pneumatic deflectors complicates construction of the printhead and requires more components. The additional components and complicated structure require large spatial volumes between the printhead and the media, increasing the ink drop trajectory distance. Increasing the distance of the drop trajectory decreases drop placement accuracy and affects the print image quality. Again, there is a need to minimize the distance the drop must travel before striking the print media in order to insure high quality images.
It can be seen that there is a need to provide a simply constructed enhanced ink drop deflector that reduces printhead maintenance; increases ink drop spacing; increases image quality; reduces the distance an ink drop must travel; and reduces the amount of vacuum required to remove non-printed ink drops.
It is an object of the present invention to provide an ink drop deflection amplifier that increases ink drop path divergence between selected and non-selected ink drops.
It is another object of the present invention to provide an ink drop deflection amplifier that reduces the distance a selected ink drop must travel before striking a recording medium.
It is another object of the present invention to provide an ink drop deflection amplifier of simple construction.
It is still another object of the present invention to provide an ink drop deflection amplifier that reduces printhead maintenance.
It is still another object of the present invention to provide an ink drop deflection amplifier that reduces ink contamination.
It is still another object of the present invention to provide an ink drop deflection amplifier that improves image print quality.
According to a feature of the present invention, an ink drop deflector mechanism includes an ink drop source and a path selection device operable in a first state to direct drops from the source along a first path and in a second state to direct drops from the source along a second path. The first and second paths diverge from the source. The mechanism also includes a system which applies force to drops travelling along at least one of the first and second paths with the force being applied in a direction so as to increase the divergence of the paths.
According to another feature of the present invention, the mechanism may include a gas source which generates a gas flow force that is applied in a direction that increases the divergence of the paths. The gas flow may be positioned between the first and second paths. The gas flow may also be substantially laminar. Additionally, the gas flow may interact with at least one of the first and second paths as the gas flow loses its coherence.
According to another feature of the present invention, the mechanism may also include a catcher. At least a portion of the system may be positioned adjacent the catcher. Alternatively, at least a portion of the system may be integrally formed in the catcher or positioned internally in the catcher.
According to another feature of the present invention, a method of increasing ink drop divergence includes providing a source of ink drops; directing the ink drops to travel in a first state along a first path and in a second state along a second path, the first and second paths diverging from the source; and causing the divergence of the paths to increase. The method may include applying a force to drops travelling along at least one of the first and second paths in order to cause the divergence of the paths to increase.
According to another feature of the present invention, the method may include generating a gas flow and applying the gas flow to drops travelling along at least one of the first and second paths in a direction that increases the divergence of the paths.
The invention, and its objects and advantages, will become more apparent in the detailed description of the preferred embodiments presented below.